Mechanical fastening systems employing two fastener elements, such as a nut and bolt, can become loosened due to vibration, temperature changes and the like, with the result that the connection may fail or not be satisfactory for the intended purpose. It is known to provide an epoxy adhesive system on at least one of the fastener elements, in order to adhesively secure the connected elements and thereby prevent unintended loosening. Mechanical fasteners are normally manufactured by someone other than the ultimate user, and it is desired that the adhesive system be applied by the manufacturer so that complications for the ultimate user are minimized. The epoxy adhesive components are normally applied in an uncured condition, and interconnection of the elements, such as by threading the nut onto the bolt, has the effect of mixing the resin components and thereby permitting them to react and cure.
Various means have been disclosed for permitting the adhesive components to be applied to the mechanical fastening elements in the uncured condition. It is known, for example, to apply in spaced relation both components of an epoxy resin system to a single one of the elements of the mechanical fastening system. Means are provided to maintain the epoxy system components separated so that unintended or accidental mixing and resultant curing is prevented. It is known, for example, to provide each of the components of the epoxy system with a photocurable additive which forms a frangible skin. The skin has sufficient structural integrity to withstand the stresses which may arise during shipment and handling, but yet will be readily ruptured and thereby allow the components to be mixed and ultimately cured when the fastener elements are combined.
Formation of the rupturable skin by the addition of a radiation curable film forming material is known, and the film forming agent may be the same for both components of a two-part epoxy resin system comprising a resin and a hardener. A photoinitiator is also customarily provided in order to enhance formation of the skin upon exposure to ultraviolet radiation.
A wire connector is a well-known means for securing together the ends of wires. A wire connector typically comprises a plastic or like insulating housing which is open at one end. A coil spring of somewhat hourglass shape is typically provided in the cavity of the housing and has the purpose of grasping the usually twisted together ends of the wires in order to draw them into the wire connector. A wire connector, like the other mechanical fasteners earlier discussed, may permit the wires to become loosened from within the wire connector, thereby permitting them to be pulled apart or to be exposed. Exposure of the wires may cause damage to the user or otherwise, and is to be avoided. For this reason, it is well-known to wrap the wire connector and a portion of the wires with an insulating adhesive tape, normally of a coated cloth or plastic composition, so that the wire connector will remain secured to the wires. Application of electrical tape is, however, a time consuming, expensive, and unreliable process.
Co-pending U.S. application Ser. No. 655,854, filed Feb. 15, 1991 by Mark Thurber and Richard M. Wallace for Adhesive systems, the disclosure of which is incorporated herein by reference, is directed to certain improvements in adhesively secured mechanical fasteners, including wire connector. That application discloses a two-component epoxy resin adhesive having an improved film-forming material for creating the frangible skin. Use of the epoxy resin adhesive with a wire connector is also disclosed.
We have found that the use of two-component epoxy resin adhesives in wire connector fasteners does have various advantages over the previous use of electrical tape. Because of the frustoconical shape of a wire connector, however, certain new problems have arisen which may adversely affect the use of the wire connector, its manufacture, and its shipability. We have discovered, for example, that filling the wire connector with the epoxy resin causes an air pocket to be formed within and/or about the spring. As discussed in the referenced application, the resin is separated from the hardener by a rupturable skin, and we have found that the relatively weak bond between the rupturable skin and the wire connector may be broken by the air pocket as it migrates within the chamber of the wire connector. It is not unusual for wire connector to be shipped by airplane, with the result that the air pocket may become relatively more mobile on account of the reduced atmospheric pressure around the connector, thereby being able to more readily separate the rupturable skin from the wire connector and permit the hardener and resin to mix and begin to cure. Once the integrity of the bond between the skin and the wire connector has been broken, then curing will begin, and the wire connector may eventually be unusable.
Yet a further problem which we have discovered concerns the deterioration in the cure speed which may occur in the event the hardener is exposed to moisture coming from the air pocket. Relatively moist air, such as may occur during the warm, humid summer months, will be dispersed within the hardener as it fills the wire connector, with the result that the cure of the resin by the hardener may take longer than desired. The rupturable skin overlying the hardener prevents it from being exposed to the ambient air, but the entrainment of moist air during the filling process still allows water to be introduced into the hardener.
Those skilled in the art will understand that a commercially acceptable adhesively securable wire connector must be able to be shipped from a remote manufacturer to the ultimate user without concern that the epoxy resin adhesive components will interact and cure during shipment, handling, and storage. The disclosed invention relates to a wire connector assembly and its method of manufacture which avoids the noted problems by filling the wire connector with the epoxy resin in an environment which is substantially devoid of air and water vapor. Substantially all of the air is evacuated from the wire connector by means of a vacuum applied prior to filling with the epoxy resin, thereby substantially eliminating the air pocket which may lift the skin and permit the introduction of moisture into the hardener.